The present invention relates to a control device for semiconductor switches of an inverter and a method for driving an inverter, in particular for operating an inverter in an emergency discharge mode.
Electric and hybrid vehicles often have electronic power switching components in the drive system between the fraction battery and the electric machine, which are generally designed as voltage-source inverters. A DC voltage intermediate circuit acts as a coupling element between the fraction battery and an inverter which can be driven for transmitting electric power from the DC voltage intermediate circuit to the electric machine.
Inverters can, for example, be designed as a full bridge circuit having a number of bridge arms, each having two semiconductor switches. The semiconductor switches of the bridge arms connected to a first output terminal of the DC voltage intermediate circuit can be designated as high-side switches, and the semiconductor switches of the bridge arms connected to the second output terminal of the DC voltage intermediate circuit can be designated as low-side switches. For example, IGBT (insulated-gate bipolar transistor) modules having a diode which is reverse-connected in parallel or MOSFETs (metal-oxide semiconductor field-effect transistors) can be used as semiconductor switches.
To drive the inverter, controls are used which generate switching signals for the semiconductor switches. In the event of a fault, various requirements are placed on the controls for reasons of safety. For example, it may be necessary to short-circuit the motor windings of the electric machine safely in the event of a fault. This can be achieved by closing all high-side switches and opening all low-side switches (or vice-versa), which is also referred to as an “active short circuit.”
In addition, in the event of a fault, it is necessary to discharge the DC voltage intermediate circuit rapidly and reliably, in particular, if there is a failure of supply voltages in the control. This can be achieved via an emergency discharge. An emergency discharge of this kind is normatively requested within a maximum emergency discharge time of five seconds in order to be able to ensure the electrical operating safety of the vehicle.
The publication US 2005/0231171 A1 discloses an electrical drive system having an electric motor, a pulse-width-modulation inverter, and an intermediate-circuit capacitor. The intermediate-circuit capacitor can be discharged in a controlled manner via an appropriate switching operation of the pulse-width-modulation inverter.